cfg80211: read wmm rules from regulatory database

ETSI EN 301 893 v2.1.1 (2017-05) standard defines a new channel access
mechanism that all devices (WLAN and LAA) need to comply with.
The regulatory database can now be loaded into the kernel and also
has the option to load optional data.
In order to be able to comply with ETSI standard, we add wmm_rule into
regulatory rule and add the option to read its value from the regulatory
database.

Signed-off-by: Haim Dreyfuss <haim.dreyfuss@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>
[johannes: fix memory leak in error path]
Signed-off-by: Johannes Berg <johannes.berg@intel.com>